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Towards a library of synthetic galaxy spectra and preliminary results of
classification and parametrization of unresolved galaxies for Gaia | | P. Tsalmantza
; M. Kontizas
; C. A. L. Bailer-Jones
; B. Rocca-Volmerange
; R. Korakitis
; E. Kontizas
; E. Livanou
; A. Dapergolas
; I. Bellas-Velidis
; A. Vallenari
; M. Fioc
; | | Date: |
15 May 2007 | | Subject: | Astrophysics (astro-ph) | | Abstract: | Aims:The Gaia astrometric survey mission will, as a consequence of its
scanning law, obtain low resolution optical (3300-1000 nm) spectrophotometry of
several million unresolved galaxies brighter than V=22. We present the first
steps in a project to design and implement a classification system for these
data. The goal is both to determine morphological classes and to estimate
intrinsic astrophysical parameters via synthetic templates. Here we describe
(1) a new library of synthetic galaxy spectra, and (2) first results of
classification and parametrization experiments using simulated Gaia
spectrophotometry of this library. Methods:We have created a large grid of
synthetic galaxy spectra using the PEGASE.2 code, which is based on galaxy
evolution models that take into account metallicity evolution, extinction
correction, emission lines (with stellar spectra based on the BaSeL library).
Our classification and regression models are Support Vector Machines (SVMs),
which are kernel-based nonlinear estimators. Results:We produce a basic library
of about 4000 zero redshift galaxy spectra covering the main Hubble types over
wavelength range 250 to 1050 nm at a sampling of 1 nm or less. It is computed
on a regular grid of four key astrophysical parameters for each type and for
intermediate random values of the same parameters. An extended library
reproduces this at a series of redshifts. Initial results from the SVM
classifiers and parametrizers are promising, indicating that Hubble types can
be reliably predicted and several parameters estimated with low bias and
variance. Comparing the colours of our synthetic library with Sloan Digital Sky
Survey (SDSS) spectra we find good agreement over the full range of Hubble
types and parameters. | | Source: | arXiv, arxiv.0705.2152 | | Services: | Forum | Review | PDF | Favorites | |
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